1. Field of the Invention
The invention relates to a method for carrying out a so-called ‘blind handover’ in an intersystem and interfrequency handover in mobile communication systems, in particular in inhomogeneous network structures of the participating mobile communication systems.
2. Description of the Prior Art
In the case of inhomogeneity of the different network structures, i.e. different frequency positions or coverage areas of the participating networks, no ensurance for the successful completion of the HO can be given in a so-called blind handover (HO).
The specification currently in effect provides that, for example, in a handover between a UMTS layer and a GSM layer, per UMTS cell, one HO candidate for a blind handover can be configured. In this case it is assumed that the coverage area of the target cell agrees with the source cell. Stated differently, the coverage area of the particular cell of the UMTS and of the GSM network are congruent at the site of the handover. Otherwise the resulting situation is ambiguous. The consequence would be an HO error and therewith the risk of losing the connection (call drop).
To avoid these problems in a blind handover, so-called dual mobile subscriber terminal sets, i.e. mobile telephones with two separate transmitting/receiving devices can be utilized, which are capable of operating simultaneously at two frequencies or in two mobile networks.
The signaling between subscriber terminal set and the participating network nodes, such as for example base stations, RNC (Radio Network Controller) and the mobile switching centers (UMSC) of the participating mobile communication networks, exchanged during a handover, is not subject matter of the method described here. It is therefore not further discusssed in the following.